Potential COVID-19 outbreak in fire camp: Scenario analysis and implications

Wildfire response is a mission critical area for the USDA Forest Service, and the interagency fire community is facing an uncertain season due to complications from COVID-19. One of the risks posed to fire response by COVID-19 is rapid outbreak of infection in a traditional large fire camp, where high-density living and working conditions, limited hygiene, and a transient workforce can create the ideal conditions for the spread of disease.

To better understand this risk and to support risk-informed decision making, the COVID-19 Fire Modeling Team modeled the potential for COVID-19 spread in fire camp under a range of fire scenarios. The analysis also explores the efficacy of screening and social distancing. Results underscore the importance of deploying these risk mitigation measures and provide insights into how characteristics of a wildfire incident factor into the effectiveness of these measures. The study is identified as Influential Scientific Information, and in addition to blind peer review was reviewed by multiple experts in public health, infectious disease, epidemiological modeling, and fire operations.

The COVID-19 Fire Modeling Team is comprised of experts in the fields of risk management, epidemiological modeling, and fire operations data from the USDA Forest Service Rocky Mountain Research Station and Colorado State University. The Team has and will continue to update the model throughout the fire season as more information becomes available. In addition, the Team has developed an online dashboard intended to provide useful information and tools to support fire manager assessment of COVID-19 risk.

The study originated because of Matthew Thompson’s participation on the USDA Forest Service Enterprise Risk Management (ERM) Team, which was activated by the USDA Forest Service Executive Leadership Team (ELT) to support agency COVID-19 response efforts. The ERM Team serves as an advisory body to the ELT to adopt a proactive and forward-looking posture, to implement best risk management practices, to support deliberative and data-driven analysis, and to facilitate risk-informed decision making. Initial modeling and scenario analyses were undertaken to support the ELT as it evaluated wildfire response in the context of COVID-19 and engaged in strategic planning.

Approach

The study analyzed the impact of interventions on wildland firefighter health and workforce availability in the setting of a single large wildland fire camp. The modeling quantified the potential for COVID-19 outbreak in that setting, and how outbreak dynamics may vary due to implementation of two risk mitigation measures: screening and social distancing. Specifically, the analysis adapted a peer-reviewed epidemiological model of COVID-19 to the context of a wildfire incident where the population changes over time.

The team analyzed a range of fire scenarios with different fire characteristics (assignment timing, personnel, and duration), infection rates, and percentages of arriving individuals that are infected.

The models were built using parameters from the peer-reviewed literature on COVID-19 as well as expert-informed assumptions regarding best and worst case scenarios for infection fatality rates due to significant unknowns regarding the impact of fatigue and smoke exposure on COVID-19 risk to firefighters.

The model was applied to population data (e.g. number of personnel assigned, how long they were on site) from three recent historical wildfires to illustrate potential outbreak dynamics. The analysis was deliberately limited in scope because of the objective to assess plausible disease dynamics and qualitative differences in interventions. Results should not be interpreted as making a prediction about any events in the current or coming fire seasons, but can be used to inform the fire community in an effort to improve overall firefighter safety.

Key Findings

• Mildly symptomatic, asymptomatic, and pre-symptomatic cases, along with possible misattributions of symptoms as typical due to exertion and smoke exposure, suggest the possibility of an infected individual arriving at a large fire incident; this could lead to a rapid outbreak with widespread infection.
• Aggressive screening to initially isolate infected individuals can reduce the total number of infections, but the benefits diminish as incident duration increases due to potential for screening errors and subsequent transmission.
• Aggressive social distancing measures (e.g., ”module as one”, remote briefings) may be more effective at reducing the total number of infections.
• The best case scenario assumes screening and social distancing are implemented jointly and effectively, which may significantly reduce but not eliminate risk.
• Results of the COVID-19 fire camp scenario analysis are intended to be illustrative rather than predictive, are designed to support identification of suitable and effective risk mitigation measures, and will be updated over time in response to new information.